1. Field of the Invention
The present invention relates to a hammer movement detection apparatus for use in the detection of a performance state in a keyboard musical instrument such as an automatic piano or the like.
2. Prior Art
Conventionally, in keyboard musical instruments such as automatic pianos or the like, the detection of hammer operations was carried out in order for the purpose of the detection of a performance state, the recording of a performance state, or the control of the reproducing of a performance or the like. An example of the structure of a detecting mechanism for the detection of such hammer operations is shown in FIG. 7.
The detecting mechanism shown in FIG. 7 is applied to the actuation control of a key 2 of a grand piano 1 which is a keyboard type musical instrument. Herein, a pair of photointerruptors 5, 5 are provided within the swinging area of a hammer shank 4, to which a hammer 3 which strikes string 9 is attached, and above this shank, and a shutter 6 is attached to this hammer shank 4. This shutter 6 sequentially interrupts these photointerruptors 5, 5 based on the swinging of the hammer shank 4. The velocity of the hammer 3 is detected in accordance with the difference in period between each interrupting period in which the photointerruptors 5, 5 are sequentially interrupted, and the string striking velocity is estimated from the detected hammer velocity. Based on this string striking velocity, the point in time at which the string is struck and the striking strength are calculated, and thereby the operational state of hammer 3 is detected. The detection signal which is output from the photointerruptors 5, 5 which detect the operational state of hammer 3 in this manner, is supplied to a control circuit (not shown in the diagram) through the medium of optical fiber 7, and by means of this control circuit the above-mentioned string striking velocity and string striking strength are obtained. In this type of conventional technology the following problems occur.
(1) In order to insert the shutter 6 into the hammer shank 4 an attachment hole must be provided in this shank 4 in advance, and the operations involved in the attachment of the shutter 6 to the hammer shank 4 make the overall assembly more difficult.
(2) Furthermore, in the above-mentioned grand piano 1, in the case in which the action mechanism 8 which includes the hammer 3 and the hammer shank 4 and the like is to be adjusted, it is necessary to remove the mechanism 8 from the grand piano 1 each time such adjustment is to be made. However, a pin board 11 which is provided along frame 10 which supports strings 9 is positioned above the action mechanism 8, and the space between this pin board 11 and the action mechanism 8 is extremely narrow. In this type of positional relationship, when photointerruptors 5, 5 and optical fiber 7 are included in the upper part of the action mechanism 8, this serves to make the gap between this mechanism and the pin board 11 even more narrow. As a result, in the case in which the action mechanism 8 is inserted or removed, there is a danger that the mechanism will make contact with this pin board 11 and will thus be damaged.
As a means to solve these problems, the following methods have been considered. A method is possible in which the inserted position of the action mechanism 8 is lowered by a certain number of millimeters; a method is also possible in which the position of the attachment hole on the hammer shank 4 is moved a number of millimeters further from the hammer wood 12; and finally, a method is possible in which the mounting board 13 is made thinner by 0.5-1 millimeter. However, in the case in which these methods are adopted, the touch of the keys 2 is affected in small ways, and thus an effect is produced which is not desirable for musical instruments.
(3) In addition, in the above described action mechanism 8, the optical fibers 7 include wiring, so that a high degree of assembly accuracy is required, and thus the ease of the assembly is negatively affected, and by means of this an increase in the number of production processes is likely.